Viscous aqueous solutions are employed in many processes. For example, they are employed to fracture subterranean formations penetrated by a borehole for increasing the production of petroleum fluids, e.g. crude oil and natural gas. Viscous aqueous solutions are also employed in the secondary recovery of oil from oil bearing subterranean formations by fluid drive processes. Also, various drilling fluids are based upon viscous aqueous liquids.
In all of these processes it is oftentimes desirable to decrease the viscosity of the viscous aqueous solution after a period of time to permit clean up of the formation, disposal of the aqueous solution and the like. Many "breakers" have been developed to cause a degradation of various thickening agents in such processes. However, most of these breakers immediately start to degrade the polymer thereby lowering the efficiency of the process. Therefore, these breakers in many instances can only be employed below critical elevated temperature levels or must be injected in a secondary fluid to contact the viscous fluid in its subterranean location. There is a need for a viscous aqueous system which can be employed at an elevated temperature and which will maintain a certain viscosity range for a certain period of time and then thereafter break to permit easy recovery and clean up of a formation. The present invention concerns such a discovery.